The disclosed invention generally relates to video circuits, and is particularly directed to a digital circuit for compensating the apparent reduced intensity of isolated pixels on a raster scan video display.
The availability of relatively inexpensive data processing capabilities has resulted in the wide use of raster scan cathode ray tube (CRT) video displays. A common characteristic of substantially all CRT video displays is that a spot or pixel is not a circular region of uniform intensity. Typically, a pixel is a generally circular region with a Gaussian distribution of intensity whereby intensity is greatest at the center and decreases toward the periphery of the pixel region. As a result of this characteristic, an area having a single pixel with at most one or two adjacent illuminated pixels appears to the viewer as being dimmer than an area having several adjacent illuminated pixels. Alphanumeric characters therefore do not appear as uniformly illuminated distinct characters. The apparent intensity differences between different portions of alpha numeric characters may readily result in viewer discomfort, eyestrain and/or misinterpretation.
The problems associated with non-uniform pixel intensity are particularly aggravated in low cost CRT displays which utilize video drivers having inexpensive circuitry to minimize cost, which almost always means reduced bandwidth. Further, the less expensive video mixers also tend to deteriorate the video signal.
The problems associated with non-uniform pixel intensity are typically reduced by increased bandwidth and more expensive CRT display circuitry. However, that approach is of no help to less expensive CRT displays.